1. Field of the Invention
Embodiments of the present invention relate to an electronic component formed of a plurality of stacked semiconductor packages, and a method of forming the electronic component.
2. Description of the Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
While a wide variety of packaging configurations are known, flash memory storage cards may in general be fabricated as system-in-a-package (SiP) or multichip modules (MCM), where a plurality of die are mounted on a substrate. The substrate may in general include a rigid base having a conductive layer etched on one or both sides. Electrical connections are formed between the die and the conductive layer(s), and the conductive layer(s) provide an electric lead structure for integration of the die into an electronic system. Once electrical connections between the die and substrate are made, the assembly is then typically encased in a mold compound to provide a protective package.
Flash memory modules may either be portable, as in the case of a land grid array (LGA) package, or dedicated, as in the case of a ball grid array (BGA) package. Portable flash memory modules are fabricated with contact pads that allow the modules to be used as removable memory. They may be inserted into a slot in a host device, whereupon the contact pads are brought into pressure contact with a printed circuit board in the host device to allow communication between the memory module and host device. Dedicated memory modules on the other hand are soldered, or otherwise permanently affixed to the printed circuit board of a host device.
A cross-section of a conventional BGA package 40 is shown in FIG. 1. One or more memory die 20 and a controller die 22 are mounted on a substrate 24 in a stacked configuration. Generally, the substrate 24 may be formed of a rigid core 28, of for example BT (Bismaleimide Triazine) laminate. Thin film copper layer(s) 30 may be formed on the top and bottom surfaces of the core in a desired electrical lead pattern using known photolithography and etching processes. Areas of the conductance pattern may be plated to receive solder balls 32 or other soldered contacts.
The substrate may be coated with a solder mask 36 to insulate and protect the electrical lead pattern formed on the substrate. The die may be electrically connected to the substrate by wire bonds 34. Vias (not shown) are formed through the substrate to allow electrical connection of the die through the substrate to the solder balls 32. Once the die are electrically connected, the package may be encapsulated in a mold compound 38 to form the package 40. The package 40 may thereafter be mounted by the solder balls 32 to a printed circuit board within a host device (not shown) in a known reflow process.
There is an ever-present drive to increase storage capacity within memory modules. One method of increasing storage capacity is to increase the number of memory die used within the package. In portable memory packages, the number of die which may be used is limited by the thickness of the package, which must not exceed a thickness of a standard-sized slot in the host device within which the memory module is received.
However, even where the thickness of a package is not limited by standard, as in a dedicated memory module, typically no more than 4 or 5 die may be stacked within a given package. The more die that are added within a package, the greater the likelihood that one or more of them will be damaged during human or automated assembly. And as the number of die goes up, package yields go down. If a single die within a package is faulty, the package must be discarded, and the good die wasted. Moreover, large numbers of die within a package draw a significant amount of current during testing and operation to power up the package.
It is therefore known to stack semiconductor packages together. For example, U.S. Pat. No. 6,407,448 entitled, Stackable Ball Grid Array Semiconductor Package and Fabrication Method Thereof, discloses a support structure within which a semiconductor die is seated. The support structure has metal traces formed on its bottom surface. A second layer of traces are then affixed on top of the die using adhesive, and connected to the die and support structure. Solder balls are then provided on top of the second layer of metal traces. A second package may then be stacked atop the first package by soldering the solder balls of the first package to the metal traces on the bottom surface of the second package.
Conventional stacked semiconductor packages have a variety of drawbacks. For example, in the design shown in the above-described U.S. Pat. No. 6,407,448, there is significant additional structure required to make the packages stackable. This significant additional structure increases the processing steps necessary to fabricate the package assembly, and adds time and expense to the fabrication process.